The present invention relates to a semiconductor device having a contact hole (connection hole) formed in an insulating film on a substrate. More particularly, the present invention relates to a semiconductor device having a semiconductor memory such as a DRAM or ferroelectric memory wherein a semiconductor element and a capacitor are electrically connected to each other via a plug within the contact hole and a manufacturing method therefor.
As recent semiconductor memory devices have increased in integration scale, attention has been given to technology for integrating, in a semiconductor substrate, a capacitor having a capacitor insulating film made of a dielectric with a dielectric constant of 30 or more (hereinafter referred to as a high dielectric), thereby providing a sufficient amount of charge accumulated in the capacitor used in a memory cell. Attention has also been given to a so-called ferroelectric memory using a ferroelectric in a capacitor insulating film as a nonvolatile memory operable with a low voltage at a high speed. As a high dielectric or ferroelectric, there has been used a dielectric material composed of a metal oxide such as Ta2O5, SrBi2Ta2O9, or BaxSr1xe2x88x92xTiO3 (where x satisfies 0xe2x89xa6xxe2x89xa61), so that the development of technology for integrating such a dielectric into a semiconductor substrate is essential to the implementation of a ferroelectric memory.
A description will be given to a conventional semiconductor memory device with reference to the drawings.
FIG. 9 shows a cross-sectional structure of the conventional semiconductor memory device. As shown in FIG. 9, a transistor 107 is formed in the region of a substrate 101 made of p-type silicon doped with a group III element which is isolated by an isolation film 102. The transistor 107 is composed of: a gate electrode 104 made of polysilicon and formed on the substrate 101 via a gate insulating film 103 made of a silicon oxide (SiO2); a source region 106; and a drain region 105. Each of the source region 106 and drain region 105 is formed in an upper portion of the substrate 101 along the gate length of the gate electrode 104 and doped with a group V element.
A bit line 108 made of polysilicon is formed on the source region 106. The transistor 107 and the bit line 108 are covered with a SiO2 insulating film 109. A contact hole 109a is formed in the region of the insulating film 109 overlying the drain region 105 and a plug 110 made of polysilicon is filled in the contact hole 109a. 
A capacitor 114 consisting of a lower electrode 111 made of platinum (Pt), a capacitor insulating film 112 made of SrBi2Ta2O9, and an upper electrode 113 made of platinum is formed on the insulating film 109 in such a manner as to cover the plug 110. A barrier layer 115 for preventing platinum composing the lower electrode 111 from being diffused into the plug 110 is disposed between the lower electrode 111 and the plug 110. An ohmic contact is made between the barrier layer 115 and the plug 110.
After the semiconductor memory device is formed, an annealing process is normally performed with respect to the semiconductor memory device in an oxygen atmosphere such that the capacitor 114 excellently retains its properties. In the barrier layer 115, therefore, there is used a nitride such as titanium nitride (TiN) or an oxide such as iridium oxide (IrO2) which is less likely to oxidize the surface of the plug 110 made of polysilicon and unreactive to polysilicon and platinum in the lower electrode 111 during the annealing process.
However, the conventional semiconductor memory device has the following problem. If titanium nitride is used in the barrier layer 115, the barrier layer 115 is more likely to lose its conductivity because titanium nitride is oxidized by the annealing process, so that the electric connection between the transistor 107 and the capacitor 114 becomes insufficient.
If an oxide such as iridium oxide is used in the barrier layer 115, the upper surface of the plug 110 is exposed to an oxygen plasma and oxidized during the formation of the barrier layer 115, so that the plug 110 loses its conductivity and the electric connection between the transistor 107 and the capacitor 114 also becomes insufficient. In either case, the problem is encountered that the semiconductor memory device is likely to incur a faulty operation.
It is therefore an object of the present invention to solve the aforesaid conventional problem and impart high reliability to a contact hole for providing an electric connection between a semiconductor element formed in a substrate and another semiconductor element formed on an insulating film covering the semiconductor element.
To attain the object, the present invention uses a conductive film containing a platinum group element to compose a plug formed in the contact hole as a connection hole. In addition, the present invention provides a barrier layer made of a metal nitride between the substrate and the plug.
Specifically, a first semiconductor device according to the present invention comprises: a substrate formed with a semiconductor element; an insulating film formed on the substrate, the insulating film having a connection hole and covering the semiconductor element; an underlying conductive film formed in at least a lower portion of the connection hole and electrically connected to the semiconductor element; and a conductive film formed in an upper portion of the connection hole and containing a platinum group element.
In the first semiconductor device, each of the underlying conductive film formed in at least the lower portion of the connection hole and the conductive film formed in the upper portion of the connection hole contains a platinum group element, so that the underlying conductive film and the conductive film are not oxidized or, if oxidized, retain conductivity in an annealing process performed in an oxygen atmosphere during the manufacturing of the first semiconductor device. As a result, an excellent electric connection is maintained among the underlying conductive film, the conductive film, and the semiconductor element, which improves the reliability of the device.
In the first semiconductor device, the connection hole preferably has a depth equal to or larger than a minimum diameter of the connection hole. This increases the scale of integration of the semiconductor elements, since the aspect ratio of the connection hole is higher than 1.
Preferably, the first semiconductor device further comprises a dielectric film formed over the conductive film. In the arrangement, the conductive film contains a platinum group element so that the upper end of the conductive film as the plug is used as the lower electrode of the capacitor without any alteration. This allows the omission of the step of forming the lower electrode and reduces the size of the capacitor formed. If the dielectric film is made of a ferroelectric, a nonvolatile memory device can be implemented.
In the first semiconductor device, the conductive film preferably expands over the portion of the insulating film surrounding the connection hole and has a top surface higher in level than an upper end of the connection hole. In the arrangement, the upper end of the conductive film protrudes from the upper end of the connection hole, which renders the upper end of the conductive film more likely to be used as the lower electrode of the capacitor. If an electroplating method using the underlying conductive film as an electrode is used, the conductive film forming the plug can be formed promptly on the underlying conductive film.
In this case, the semiconductor device preferably further comprises a dielectric film formed over the conductive film. In the arrangement, if the upper end of the conductive film is used as the lower electrode of the capacitor, the dielectric film formed over the conductive film is used as the capacitor insulating film, the upper electrode is formed on the capacitor insulating film, and the capacitor can be formed reliably over the connection hole.
In this case, the semiconductor device preferably further comprises a capacitor formed on the insulating film, the capacitor having a lower electrode composed of the conductive film and a capacitor insulating film composed of the dielectric film. If a transistor is used as the semiconductor element in the arrangement, a semiconductor memory device having excellent conduction between the transistor and the capacitor can be implemented.
In the first semiconductor device, the conductive film is preferably filled in the upper portion of the connection hole. This reduces the electric resistance of the conductive film and improves the operating properties of the device.
In this case, the conductive film preferably expands over the portion of the insulating film surrounding the connection hole and has a top surface higher in level than an upper end of the connection hole.
In this case, the first semiconductor device preferably further comprises a dielectric film formed over the conductive film.
In this case, the first semiconductor device preferably further comprises a capacitor formed on the insulating film, the capacitor having a lower electrode composed of the conductive film and a capacitor insulating film composed of the dielectric film.
In this case, the conductive film preferably has a substantially flat top surface. In the arrangement, even when a dielectric film is formed on the conductive film, the resulting dielectric film has a uniform thickness. If the dielectric film is used as the capacitor insulating film, the electric properties of the capacitor are improved.
In the first semiconductor device, the underlying conductive film is preferably formed on a sidewall portion of the connection hole and at least a part of an end face of the underlying conductive film is substantially continued to an end face of the conductive film. In the arrangement, if the upper end (upper surface) of the conductive film is covered with a dielectric film, the underlying conductive film and the conductive film can be covered collectively, which improves the usability of the dielectric film as the capacitor insulating film.
In this case, the conductive film is preferably filled in the upper portion of the connection hole.
A second semiconductor device according to the present invention comprises: a substrate formed with a semiconductor element; an insulating film formed on the substrate, the insulating film having a connection hole and covering the semiconductor element; a conductive film formed in an upper portion of the connection hole and containing a platinum group element; and a barrier layer formed in a lower portion of the connection hole, the barrier layer having conductivity, being electrically connected to the semiconductor element, and preventing a constituent element of the conductive film from being diffused into the substrate.
In the second semiconductor device, the conductive film containing a platinum group element is used as the plug, so that the same effect as achieved by the first semiconductor device can be achieved. Moreover, since the barrier layer for preventing the diffusion of the constituent element of the conductive film into the substrate is provided in the lower portion of the connection hole, the reaction between the platinum group element and the material of the substrate can be prevented, which further improves the operating properties of the device.
In the second semiconductor device, the barrier layer is preferably composed of a metal nitride. The arrangement surely prevents the diffusion of the platinum group element into the substrate.
The second semiconductor device preferably further comprises an underlying conductive film formed between the barrier layer and the conductive film in the connection hole and containing a platinum group element.
In the second semiconductor device, the conductive film preferably expands over the portion of the insulating film surrounding the connection hole and has a top surface higher in level than an upper end of the connection hole.
In this case, the second semiconductor device preferably further comprises a dielectric film formed over the conductive film.
In this case, the second semiconductor device preferably further comprises a capacitor formed on the insulating film, the capacitor having a lower electrode composed of the conductive film and a capacitor insulating film composed of the dielectric film.
In the second semiconductor device, the conductive film preferably has a substantially flat top surface.
In the semiconductor device, the underlying conductive film is preferably formed on a sidewall portion of the connection hole and at least a part of an end face of the underlying conductive film is substantially continued to an end face of the conductive film.
In this case, the conductive film is preferably filled in the upper portion of the connection hole.
A first method of manufacturing a semiconductor device according to the present invention comprises: an insulating film forming step of forming an insulating film over a substrate formed with a semiconductor element such that the semiconductor element is covered with the insulating film; an underlying conductive film forming step of forming, after forming a connection hole in the insulating film, an underlying conductive film containing a platinum group element in at least a lower portion of the connection hole such that the underlying conductive film is electrically connected to the semiconductor element; and a conductive film forming step of forming a conductive film containing a platinum group element in an upper portion of the connection hole by an electroplating method using the underlying conductive film as an electrode.
In accordance with the first method of manufacturing a semiconductor device, the use of, e.g., a sputtering process in the underlying conductive film forming step allows the underlying conductive film to be formed over the entire surface of the insulating film including the sidewall portions of the contact hole and in the lower portion of the contact hole except in the upper portion thereof. If the underlying conductive film is used as the cathode in the subsequent step of forming a conductive film using the electroplating method, therefore, the connection hole can be filled promptly and reliably because the aspect ratio is higher than 1 even when it is difficult to fill the conductive film containing a platinum group element in the connection hole by physical vapor deposition such as sputtering.
In the first method of manufacturing a semiconductor device, the electroplating method is preferably implemented by intermittently applying a voltage to the underlying conductive film. This ensures the formation of the conductive film since the ion concentration of a platinum group element is recovered during periods during which the application of a voltage to the underlying conductive film is intermitted.
In the first method of manufacturing a semiconductor device, the underlying conductive film forming step preferably includes the step of forming the underlying conductive film on a sidewall portion of the connection hole, the method further preferably comprising, after the conductive film forming step, a patterning step of pattering the underlying conductive film and the conductive film such that at least a part of an end face of the underlying conductive film is substantially continued to at least a part of an end face of the conductive film. In the arrangement, if the upper end (upper surface) of the conductive film is covered with a dielectric film, the underlying conductive film and the conductive film can be covered collectively, which improves the usability of the dielectric film as the capacitor insulating film.
Preferably, the first method of manufacturing a semiconductor device further comprises, after the patterning step, the step of forming a dielectric film on the conductive film. In the arrangement, the upper end of the conductive film containing a platinum group element can be used as the lower electrode of the capacitor without any alteration. This allows the omission of the step of forming the lower electrode and reduces the size of the capacitor formed. If the dielectric film is made of a ferroelectric, a nonvolatile memory device can be implemented.
A second method of manufacturing a semiconductor device according to the present invention comprises: an insulating film forming step of forming an insulating film over a substrate formed with a semiconductor element such that the semiconductor element is covered with the insulating film; a barrier layer forming step of forming, after forming a connection hole in the insulating film, a barrier layer in a lower portion of the connection hole, the barrier layer having conductivity, preventing a constituent element of the conductive film formed in the connection hole from being diffused from the conductive film into the substrate, and being electrically connected to the semiconductor element; and a conductive film forming step of forming a conductive film containing a platinum group element in an upper portion of the connection hole.
In accordance with the second method of manufacturing a semiconductor device, the barrier layer for preventing the diffusion of the constituent element of the conductive film formed in the connection hole from the conductive film into the substrate is formed in the lower portion of the connection hole, so that the second semiconductor device according to the present invention is implemented reliably.
In the second method of manufacturing a semiconductor device, the conductive film forming step preferably includes the steps of: forming an underlying conductive film containing a platinum group element on the barrier layer in the connection hole except in the upper portion of the connection hole; and forming the conductive film in the upper portion of the connection hole by an electroplating method using the underlying conductive film as an electrode. If the underlying conductive film is thus formed over the entire surface of the insulating film including the sidewall portions of the connection hole and over the top surface of the barrier layer except in the upper portion of the connection hole and the underlying conductive film is used as the cathode, the connection hole can be filled promptly and reliably with the conductive film even when it is difficult to fill the conductive film containing a platinum group element in the connection hole by physical vapor deposition such as sputtering.
A third method of manufacturing a semiconductor device according to the present invention comprises: an insulating film forming step of forming an insulating film over a substrate formed with a semiconductor element such that the semiconductor element is covered with the insulating film; an underlying conductive film forming step of forming, after forming a connection hole in the insulating film, an underlying conductive film containing a platinum group element in at least a lower portion of the connection hole such that the underlying conductive film is electrically connected to the semiconductor element; a mask pattern forming step of forming, on the insulating film, a mask pattern having an opening located over the connection hole in the insulating film; a conductive film forming step of forming a conductive film containing a platinum group element in an upper portion of the connection hole by an electroplating method using the underlying conductive film as an electrode and using the mask pattern; and an underlying conductive film patterning step of patterning, after removing the mask pattern, the underlying conductive film such that a region of the underlying conductive film covered with the mask pattern is thereby removed.
In accordance with the third method of manufacturing a semiconductor device, the same effect as achieved by the first method of manufacturing a semiconductor device can be achieved. Moreover, since the mask pattern for masking the insulating film except for the region corresponding to the connection hole is formed after the formation of the underlying conductive film, the conductive film containing a platinum group element can be filled reliably only in the upper portion of the connection hole in accordance with the electroplating method using the underlying conductive film as a cathode in the subsequent conductive film forming step. In addition, it is no more necessary to pattern the conductive film.
The third method of manufacturing a semiconductor device preferably further comprises, between the connection hole forming step and the underlying conductive film forming step, the step of forming a barrier layer in the lower portion of the connection hole, the barrier layer having conductivity and preventing a constituent element of the conductive film from being diffused from the conductive film into the substrate. In the arrangement, the barrier layer prevents the reaction between a platinum group element and the constituent element of the material of the substrate, so that the operating properties of the device are further improved.
The third method of manufacturing a semiconductor device preferably further comprises, after the underlying conductive film patterning step, the step of forming a dielectric film on the conductive film. In the arrangement, the upper end of the conductive film containing a platinum group element can be used as the lower electrode of the capacitor without any alteration. This allows the omission of the step of forming the lower electrode and reduces the size of the capacitor formed. If the dielectric film is made of a ferroelectric, a nonvolatile memory device can be implemented.
The third method of manufacturing a semiconductor device preferably further comprises, after the underlying conductive film patterning step, the step of forming, over the conductive film, a capacitor insulating film composed of a dielectric film and an upper electrode to form a capacitor constituted by a lower electrode composed of the conductive film, the capacitor insulating film, and the upper electrode. The arrangement allows the implementation of a semiconductor memory device wherein an excellent electric connection is provided between the semiconductor element in the substrate and the capacitor on the insulating film covering the semiconductor element.